A. Hepatitis B Virus
Hepatitis B (serum hepatitis) virus is transmitted among humans and manifests as chronically debilitating infections which can result progressively in severe liver damage, primary carcinoma and death. In most cases, complete recovery from hepatitis B infections can be expected; however, large segments of the population, especially in many African and Asian countries, are chronic carriers with the dangerous potential of transmitting the disease pandemically.
Hepatitis is caused by a virus vector (hepatitis B virus or HBV) which in its whole state--the so-called Dane particle-represents the virion and consists of a nucleocapsid enclosing a DNA molecule and an envelope surrounding the nucleocapsid. Proteins associated with the virion include the core antigen (HBcAg), a DNA polymerase and the surface antigen (HBsAG) which has been found in serum of infected and carrier humans. Antibodies to HBsAG have also been found in serum HBV infected people. It is believed that HBsAG is the HBV antigen that can induce immunogenic production of antibody (anti-HBs) and thus it would be the principal in an HBV vaccine. Attention is directed to: Dane et al., Lancet 1970 (I), 695 (1970); Hollinger et al., J. Immunology 107, 1099 (1971); Ling et al., J. Immunology 109, 834 (1972); Blumberg, Science 197, 17 (1977); Peterson et al., Proc. Nat. Acad. Sci (USA) 74, 1530 (1977) and Viral Hepatitis, A Contemporary Assessment of Etiology, Epidemiology, Pathogenesis and Prevention. (Vyas et al., eds.) Franklin Institute Press, Philadelphia, 1978, each of which is hereby incorporated by this reference to further illustrate the background of this invention.
HBsAg is present in infected plasma predominantly in the form of spherical particles having diameters ranging from about 16 to 25 nm--the so-called "22 nm particle." These are thought to represent a noninfectious viral envelope. Because antibodies against HBsAg are protective against HBV infection, these non-infectious particles can effectively be used as a vaccine.
Inasmuch as the hepatitis B virus has not been infectious in cell culture and can only be obtained from infected humans or higher primates, means have not been available for obtaining and maintaining sufficient supplies of HBV for use in producing antigen for immunization against HBV.
The present invention provides the means and methods for producing a vaccine effective against HBV. By means of recombinant DNA technology, the gene encoding HBsAg was inserted together with appropriate translational start and stop signals under the control of an appropriate expression promoter into a replicable expression vector and the latter used to transform yeast cells. The cells, thus genetically directed, produced HBsAg directly and in particle form which, when purified, is suitable to immunize against HBV.